... except for the fact that 形容詞 (i-adjectives) and 形容動詞 (na-adjectives) are used differently from 名詞 (nouns) and 動詞 (verbs). So there needs to be some distinct

... except for the fact that 形容詞 (i-adjectives) and 形容動詞 (na-adjectives) are used differently from 名詞 (nouns) and 動詞 (verbs). So there needs to be some distinction at some point, even if at the high level, 名詞 and 形容動詞 are similarish, and 形容詞 and 動詞 are similarish. But that doesn't go beyond -ish, and it's important to know.